The present invention relates to compositions suitable for use as lubricant additives which contain an ester-substituted hindered phenol antioxidant and other additives suitable for lubricants such as a detergent or a dispersant. The present invention provides an economical antioxidant which has good performance properties when used in lubricant formulations especially for heavy duty diesel engines and passenger car crankcase.
U.S. Pat. No. 5,523,007, Kristen et al., Jun. 4, 1996, discloses a lubricant oil composition comprising a diesel engine lubricating oil and, as antioxidant, a compound of the formula 
X can be xe2x80x94CH2xe2x80x94CH2xe2x80x94C(xe2x95x90O)xe2x80x94OR and R is a straight chain or branched alkyl radical of the formula xe2x80x94CHnH2n+1 wherein n is an integer from 8 to 22.
U.S. Pat. No. 3,285,855, Dexter et al., Nov. 15, 1966, discloses stabilization of organic material with esters containing an alkylhydroxyphenyl group. The ester can have the structure 
in which x has a value of from 0 to 6, inclusively, and y has a value of from 6 to 30, inclusively. The xe2x80x9clower alkylxe2x80x9d groups can be t-butyl. Organic materials which can be stabilized include, among many others, lubricating oil of the aliphatic ester type, and mineral oil.
U.S. Pat. No. 5,206,414, Evans et al., Apr. 27, 1993, discloses a process for the preparation of compounds of the general formula 
A can be xe2x80x94OR4 where R4 can be C2-C45 alkyl.
The present invention provides, among other advantages, a convenient method for obtaining a certain class of hindered phenolic ester antioxidants having particularly useful properties. In particular the antioxidants (shown below), that is, those having an R3 group of 2 to 6 carbon atoms, can be conveniently prepared in a single step. In a preferred synthesis, no trans-esterification reaction is necessary, resulting in a simplified process which leads to fewer byproducts. The antioxidants thus prepared impart excellent thermal and oxidative stability to lubricant formulations and show excellent performance in seal durability tests.
A composition comprising;
(A) at least one antioxidant of the formula 
xe2x80x83wherein R3 is an alkyl group containing 2 to 6 carbon atoms; and
(B) at least one component selected from the group consisting of dispersants and detergents.